1. Field of the Invention
The present invention relates to a process for forming a pattern of a semiconductor device used in a liquid crystal display apparatus and a method for producing a liquid crystal display apparatus using the process for forming a pattern, and in particular, to a process for forming a complicated pattern such as wiring in a simplified manner, and a method for producing a liquid crystal display apparatus using the process.
2. Description of the Prior Art
A method for producing a liquid crystal display apparatus uses a photolithography technique and a dry etching technique to produce an integrated circuit. To reduce process steps for producing the integrated circuit in the process for producing a liquid crystal display apparatus, methods for reducing the number of the total process steps for forming patterns such as wirings are exercised as well as methods to reduce the production cost thereof.
Among a variety of proposals to greatly reduce the production cost, one method proposes that two or more PR process steps required in the conventional technique can be reduced to only one process step.
That is, the first conventional example (JP-A-2000-206571) applies the above-stated method to a manufacturing process of an inversely staggered thin film transistor (hereinafter referred to as a xe2x80x9cTFTxe2x80x9d), and FIGS. 1A to 2B are schematic cross sectional views of associated regions in a vicinity of a TFT showing main process steps of the manufacturing process.
As shown in FIG. 1A, a gate electrode 533 and a gate insulating film 534 are formed on a first transparent electrode 501, and then an amorphous silicon (a-Si) film 541, an n+type amorphous silicon (n30 type a-Si) film 542 and a metal film 543 for source/drain electrodes are deposited in order thereon. A photosensitive film is further coated on the metal film 543 to a thickness of from 1 to 2 xcexcm and then exposed and developed to form a thick photosensitive film pattern 527 having a thick film thickness and a thin photosensitive film pattern 526 having a thin film thickness.
As shown in FIG. 1B, the metal film 543 is etched and removed by using the thick photosensitive film pattern 527 and the thin photosensitive film pattern 526 as a mask to expose the n+ type a-Si film 542.
As shown in FIG. 2A, the n30  type a-Si film 542 and the a-Si film 541 thereunder are subjected to dry etching step together with the thin photosensitive film pattern 526 and the metal film 543 is exposed between the thick photosensitive film patterns 527 left after the dry etching.
As shown in FIG. 2B, the metal film 543 and the n+ type a-Si film 542 are etched and removed by using the remaining thick photosensitive film pattern 527 as a mask. At this time, a part of the a-Si film 541 is simultaneously etched.
As described above, two different patterns of the film to be etched can be formed by utilizing the photosensitive film patterns 527 and 526 having different film thicknesses.
Also the following second conventional example (JP-A-2000-164584) applies the above-stated method to a manufacturing process of an inversely staggered TFT, and FIGS. 3A to 3C are schematic cross sectional views of a region of a TFT, a gate terminal electrode and a drain terminal electrode showing the main process steps in the order of manufacturing process.
As shown in FIG. 3A, a gate electrode 633, a gate terminal electrode 693 and a gate insulating film 634 are formed on a first transparent substrate 601, and an a-Si film 641, an n type a-Si film 642 and a metal film for source/drain electrodes are sequentially deposited thereon. The metal film and the n+ type a-Si film 642 thereunder are then patterned to have the same pattern to form a source electrode 659 and an ohmic layer thereunder, a drain electrode 658 and an ohmic layer thereunder, and a drain terminal electrode 678 and an ohmic layer thereunder. After depositing a passivation film 640 thereon, a resist pattern is formed such that openings are formed therein above the gate terminal electrode 693 and the drain terminal electrode 678, a thin photosensitive film pattern 626 having a thin film thickness is formed above the source electrode 659 and a separation region 660 to separate an a-Si film next thereto, and a thick photosensitive film pattern 627 having a thick film thickness is formed above the other regions.
Subsequently, as shown in FIG. 3B, the thin photosensitive film pattern 626 is etched and removed by utilizing the resist pattern while optimizing the etching conditions so as to at least remove the photosensitive film pattern 626, whereby the passivation film 640 on the drain terminal electrode 678 is completely removed and the films ranging from the passivation film 640 to a part of the gate insulating film 634 in a vertical direction on the gate terminal electrode 693 are removed.
Furthermore, as shown in FIG. 3C, both the passivation film 640 and the a-Si film 641 corresponding to the a-Si film separation region 660 are removed and simultaneously a part of the gate insulating film 634 remaining on the gate terminal electrode 693 is removed by optimizing the etching conditions.
According to the manufacturing process of the second conventional example, the contact holes on the respective electrodes are formed and the a-Si film is separated through only one PR process step by utilizing the resist film having different film thicknesses.
Techniques employed in both the first and second conventional examples described above are developed to reduce the number of manufacturing process steps in the following manner. That is, after coating a photosensitive film of a single layer on a film to be etched, a photosensitive film pattern having different film thicknesses is formed by utilizing an exposure having different amounts of light, and the film to be etched is etched by utilizing the difference in film thickness thereof.
However, in the first and second conventional examples, when the thin photosensitive film pattern out of the photosensitive film pattern is etched and removed, the thick photosensitive film pattern is also etched to have an appearance largely different from that of the thick photosensitive film pattern before being etched since the appearance of the thick photosensitive film pattern is continuously changed in accordance with passage of time during the etching. Therefore, it is expected that by using the thick photosensitive film pattern as a mask, the film to be etched is etched to have a pattern greatly different from that designed by a process designer.
An object of the invention is to provide a process for forming a pattern and a manufacturing process for producing a liquid crystal display apparatus using the same, in which in the event a film to be etched is etched by utilizing a photosensitive film pattern (hereinafter referred to as a resist pattern) having difference film thicknesses, while a thick resist portion of the resist pattern having a film thickness thicker than that of a thin resist portion thereof is being exposed to the atmosphere used for etching and removing the thin resist portion, the shape of the thick resist pattern can be maintained.
The first aspect of the process for forming a pattern in accordance with the invention comprises:
a resist pattern formation step of coating a first resist film and a second resist film in order on a film to be etched on a substrate, and further, forming a resist pattern by patterning the first resist film and the second resist film to make the first resist film broader than the second resist film while making the second resist film positioned on the first resist film;
a first patterning step of etching the film to be etched to form a first pattern in the film to be etched by using the resist pattern as a mask; and
a resist etching step of etching the resist pattern to remove at least a portion of the first resist film, the portion being not covered by the second resist film, to thereby form a remaining resist pattern consisting of the first resist film and the second resist film,
in which the resist etching step further is constructed such that the second resist film is in a state of a resist film having higher resistance against dry-etching than that of said first resist film at least during said resist etching step.
According to the first aspect of the process for forming a pattern in accordance with the invention, the remaining resist pattern is formed to have a pattern different from the resist pattern used in the first patterning step and in addition, nearly equal to the pattern of the second resist film before the resist etching step, and therefore, when subjecting the film to be etched to a second patterning step, the pattern of the second resist film can be transferred with high accuracy to the film to be etched by using the remaining resist pattern as a mask.
The second aspect of the process for forming a pattern in accordance with the invention is constructed by further adding the following construction to the first aspect of the process for forming a pattern:
in the resist pattern formation step, the resist pattern includes a first opening formed in the first resist film and a second opening formed in the second resist film, and the first opening is formed inside the second opening, and in the resist etching step, the remaining resist pattern is formed to have an overhang of the second resist film with respect to the first resist film.
According to the second aspect of the process for forming a pattern in accordance with the invention, the remaining resist pattern is formed different from the resist pattern used in the first patterning step and in addition, nearly equal to the pattern of the second resist film before the resist etching step. Therefore, when an electrically conductive film is deposited on the remaining resist pattern and the remaining resist pattern is removed together with the electrically conductive film thereon to thereby form an electrically conductive pattern connected to the film to be etched. In this case, the electrically conductive pattern is formed as a result of the second patterning step in the one photoresist step such that the pattern of the second resist film is transferred with high accuracy to the electrically conductive pattern.
The third aspect of the process for forming a pattern in accordance with the invention is constructed by further adding the following construction to the first aspect of the process for forming a pattern:
a gate wiring and a gate insulating film covering the gate wiring are formed on the substrate and under the film to be etched;
the film to be etched is a laminated film formed by depositing a semiconductor film, a semiconductor film doped with impurities and a metal film for source/drain electrodes in order on the gate insulating film; and
the resist pattern is formed on the laminated film.
According to the third aspect of the process for forming a pattern in accordance with the invention, the remaining resist pattern is formed to have a pattern different from the resist pattern used in the first patterning step and in addition, nearly equal to the pattern of the second resist film before the resist etching step, and therefore, when subjecting the film to be etched to a second patterning step, the pattern of the second resist film can be transferred with high accuracy to the film to be etched by using the remaining resist pattern as a mask.
The fourth aspect of the process for forming a pattern in accordance with the invention is constructed by further adding the following steps to the third aspect of the process for forming a pattern:
a step of depositing a protective insulating film on the gate insulating film after removing the remaining resist pattern used in a second patterning step, the second patterning step being performed such that the laminated film is etched using the remaining resist pattern as a mask;
a step of coating a third resist film and a fourth resist film in order on the protective insulating film and patterning the third resist film and the fourth resist film to make the third resist film broader than the fourth resist film while making the fourth resist film positioned on the third resist film to form a second resist pattern consisting of the third resist film and the fourth resist film, the second resist pattern having an opening therein;
a step of at least removing associated portion of the protective insulating film using the second resist pattern as a mask to expose a surface of an electrically conductive layer consisting of the laminated film and positioned below the protective insulating film; and
a step of selectively etching the third resist film out of the second resist pattern to make an overhang of the fourth resist film with respect to the third resist film in the opening,
in which the overhang is formed such that the fourth resist film is made to include silicon atoms to change the fourth resist film into a silicon-doped fourth resist film and then, the silicon-doped fourth resist film is modified to a silicon oxide film through a plasma treatment performed using a mixed gas containing at least oxygen, and thereafter, an associated part of the third resist film is removed in a lateral direction.
According to the fourth aspect of the process for forming a pattern in accordance with the invention, the opening is formed as a result of the first patterning step in the protective insulating film exposing the surface of the laminated film by using the second resist pattern and further, the overhang of the fourth resist film with respect to the third resist film is formed around the opening. Therefore, when a second electrically conductive film is deposited covering the opening, the third and fourth resist films, and then, the third and fourth resist films are removed together with the second electrically conductive film thereon to thereby form a second electrically conductive pattern connected to the laminated film. In this case, the second electrically conductive pattern is formed as a result of the second patterning step such that the pattern of the fourth resist film is transferred with high accuracy to the second electrically conductive pattern.